Abstract Ocean is generally a major barrier of migration for most flightless land animals; however, terrestrial flightless insects often demonstrate wide range distribution across oceans. To elucidate the mechanism of flightless insects to expand their distribution over the sea, we measured the survivorship of nine species of coastal beetles on seawater (i.e. seawater tolerance). We observed that two out of nine coastal beetle species showed over 10 days of median survival days (50% death days), and nearly 1 month of maximum survival days. From the unexpectedly long survival on the surface of seawater, we propose the hypothesis of “floating dispersal,” where individuals simply float on the sea surface and cross the ocean with currents. This mode can provide a novel explanation of transoceanic migration/distribution of flightless animals.
To overview the morphological and ecological diversification within a species of phytophagous ladybird beetle Henosepilachna diekei, information concerning its distribution and host plant use was studied. This species was found widely in South East and South Asia from the Philippines through the Greater Sunda islands, a western part of Lesser Sundas, the Malay Peninsula to Sri Lanka. Mikania species (Asteraceae), Mikania micrantha in particular, were the most frequently used host plants, but some other plants belonging to Lamiaceae or Acanthaceae were also used by some local populations. Each population is possibly monophagous. According to morphological analyses, seven populations from four host plants at six sites on four Indonesian islands were grouped into two, one occurring on Java and Kalimantan (Borneo) and another on Sulawesi and Lombok, indicating that they were separated by the Wallace line. This morphological distinction was not correlated with the host plant use.
Abstract Divergent host specialization by phytophagous insects is often detected as local adaptation and is thought to have played an important role in their diversification even within an ecological specialist. The phytophagous ladybird beetle Henosepilachna niponica Lewis (Coleoptera: Coccinellidae) predominantly depends on thistles ( Cirsium spp., Asteraceae). The distribution of H. niponica occupies multiple areas dominated by different thistle species. This implies the possibility of the occurrence of host‐associated divergent specialization of H. niponica . In this study, we investigated the pattern of host‐use ability of three allopatric H. niponica populations (Aomori, Iwate, and Yamagata) on three thistle species – Cirsium alpicola Nakai, Cirsium nipponicum (Maxim.) Makino, and Cirsium tonense Nakai – under laboratory conditions. The results displayed asymmetric local adaptation by the beetles. The adults and larvae of the Aomori population showed sufficient acceptance and performance on C. nipponicum and C. tonense , the hosts of the Iwate and Yamagata populations, respectively. On the other hand, the Iwate and Yamagata populations fed small amounts of and performed poorly on C. alpicola , the host of the Aomori population. In contrast, the adults from all the populations clearly preferred feeding on C. nipponicum or C. tonense to C. alpicola . We concluded that the small but significant population differentiation and asymmetric local adaptation by beetles to congeneric host plant species could be a sign of the earliest stage of population divergence by divergent natural selection, given that these divergences will act as ‘immigrant inviability’ and ‘habitat isolation’ at least asymmetrically when these populations come into contact.
Abstract Recent developments in, and widespread availability of, platforms, technologies, and computer software and hardware have enhanced the use of genetic markers to address major scientific questions in non‐model organisms, even by researchers with limited expertise in genomics. However, there are few studies investigating the genomes of non‐model insects using these approaches. This review discusses the application of next‐generation sequencing (NGS) technologies to the study of genomes of wild organisms. We first introduce currently available NGS‐based methods—including restriction site‐associated DNA sequencing; multiplexed inter‐simple sequence repeat genotyping by sequencing; target capture; and amplicon, transcriptome, and whole genome sequencing—as useful tools for studies of non‐model insects. We also provide guidelines for first‐time users of NGS systems. In addition to the massive amount of information that it provides, a major advantage of NGS data is the scalability to future research projects. Studies using NGS technology can answer questions related to basic entomology by focusing on the unique nature of non‐model insects in wild environments in a way that is not possible for model organisms.
Abstract Biological diversification often includes burst of lineage splitting. Such “radiation” has been known to act as evolutionary arenas with the potential to generate unique phylogenetic clusters and further novel groups. Although these radiations when accompanied by ecological diversification, so‐called “adaptive radiation” have persisted as a central premise in evolutionary biology, the ecological and genetic mechanism of such rapid diversification has remained unclear. There are several critical definitions for the pattern of adaptive radiation, and those provide delimitation of adaptive and non‐adaptive radiation. That being said, only a few studies have provided any clear demarcations in our understanding of the adaptive and non‐adaptive causes of radiation from the mechanism of speciation. Here, we review the current consensus for the causes of adaptive radiation, especially along with the recent theoretical synthesis of “ecological speciation.” Further, we suggest the signature of adaptive and non‐adaptive radiation in the earliest stages of diversification from the viewpoint of speciation. These criteria from the speciation view are useful to find the cases with the signatures of adaptive/non‐adaptive radiation.
Abstract This study reports genome size ( C ‐value) estimates for seven species of ladybird beetles ( C oleoptera: C occinellidae) in J apan using flow cytometry. The results demonstrated genome sizes of 1.0–1.4 G b in four closely related phytophagous ladybird beetles belonging to the H enosepilachna vigintioctomaculata species complex. These values were approximately two times larger than that of a congeneric phytophagous ladybird beetle H . vigintioctopunctata (0.66 G b), and of two very distantly related common carnivorous ladybird beetles, H armonia axyridis (0.46 G b) and C occinella septempunctata (0.42 G b). These lines of evidence suggest that rapid and large genome size increase occurred just after the branching of the common ancestor of the H . vigintioctomaculata species complex from other ladybird species.
Adaptation to different environments can promote population divergence via natural selection even in the presence of gene flow - a phenomenon that typically occurs during ecological speciation. To elucidate how natural selection promotes and maintains population divergence during speciation, we investigated the population genetic structure, degree of gene flow and heterogeneous genomic divergence in three closely related Japanese phytophagous ladybird beetles: Henosepilachna pustulosa, H. niponica and H. yasutomii. These species act as a generalist, a wild thistle (Cirsium spp.) specialist and a blue cohosh (Caulophyllum robustum) specialist, respectively, and their ranges differ accordingly. The two specialist species widely co-occur but are reproductively isolated solely due to their high specialization to a particular host plant. Genomewide amplified fragment-length polymorphism (AFLP) markers and mitochondrial cytochrome c oxidase subunit I (COI) gene sequences demonstrated obvious genomewide divergence associated with both geographic distance and ecological divergence. However, a hybridization assessment for both AFLP loci and the mitochondrial sequences revealed a certain degree of unidirectional gene flow between the two sympatric specialist species. Principal coordinates analysis (PCoA) based on all of the variable AFLP loci demonstrated that there are genetic similarities between populations from adjacent localities irrespective of the species (i.e. host range). However, a further comparative genome scan identified a few fractions of loci representing approximately 1% of all loci as different host-associated outliers. These results suggest that these three species had a complex origin, which could be obscured by current gene flow, and that ecological divergence can be maintained with only a small fraction of the genome is related to different host use even when there is a certain degree of gene flow between sympatric species pairs.
The ladybird beetles Propylea quatuordecimpunctata and P. japonica have largely overlapping distributions in northern Japan, and in the laboratory produce fertile hybrids. In this study, we surveyed the distribution and morphological differentiation of these species and the hybrids in natural populations, with a focus on western Hokkaido, northern Japan. Phenotypic analyses were conducted for 987 individuals collected at 90 localities. In addition, the nuclear internal transcribed spacer-II (ITS2) region (549 bp) and part of the mitochondrial cytochrome c oxidase subunit I (COI) gene (700 bp) were sequenced for 620 individuals from 53 localities. Analyses of both phenotypic and genotypic features discriminated two distinct entities assignable to P. quatuordecimpunctata and P. japonica. However, individuals with intermediate phenotypes and/or genotypes also occurred extensively, indicating natural hybridization. Putative P. quatuordecimpunctata individuals were collected across a wide range of altitudes (30–600 m), whereas those of P. japonica were found mostly lower than 300 m alt. In addition, P. quatuordecimpunctata was dominant in semi-open habitats shaded by canopy foliage, whereas P. japonica was frequent in more open habitats. The perceived altitudinal difference in the distributions may thus in part be a consequence of this different habitat preference, as open habitats are more common at lower altitudes in the study area.
